The present invention relates to the monitoring of audio signals, and more particularly to a dual-bar audio level meter for digital audio with dynamic range control.
Broadcast audio almost always is processed before transmission to reduce its dynamic range. There are several reasons for this practice: (1) the transmission system signal-to-noise ratio (SNR) is not great enough to handle a wide dynamic range; (2) typical listeners want limited range for most listening environments; and (3) the station may push up the average level so the station sounds louder and grabs the attention of a listener tuning across the band. This processing often is overdone, and becomes offensive to listeners who want to hear the full dynamic range.
With the advent of digital broadcasting, digital television particularly, there now is a way to accommodate both the casual listener who wants to keep the volume more or less constant and the critical listener who wants to experience the full dynamic range of a concert hall or theater. The uncompressed full range audio is transmitted along with a varying control signal that the receiver may use to automatically control the audio level. The listener may choose which way to listen depending upon the environment. The Dolby AC-3 standard for digital television in the United States of America includes a sophisticated implementation of this dynamic range control technique. In order to monitor the digital audio signal an operator uses a conventional audio level meter and monitors the signal first with the dynamic range control on and then with the dynamic range control off. This requires the operator to constantly switch between the two modes in order to monitor the digital audio signal.
What is desired is a means for monitoring digital audio signals with dynamic range control using a display that is simple to read and understand, and that presents the digital audio signals both with and without dynamic range control simultaneously.